A student wishes to light a lamp rated 12V, yet he has only a 2V rms a.c supply with variable frequency. So he attempts to step up the voltage by means of a transformer. Given Ns:Np = 6:1, resistance in the primary circuit is 70 ohm, inductance of primary coil is 0.3H, frequency f is 50Hz a.) If Ns = 600, Vs = 10V (rms), cross-sectional area of the secondary coil is 2cmx2cm, what is the maximum B-field in the iron core? i find this question really difficult, cuz my teacher uses differentiation to solve it... i wonder if there are simple ways to solve it. Thanks!